1. Field of the Invention
This invention relates to the field of hydraulic mechanisms used primarily for, but not limited to, raising and lowering truck beds. More particularly, this invention relates to a neutral stop device provided to prevent accidental lowering of the truck bed.
2. Description of the Prior Art
Hydraulic mechanisms have long been used to raise and lower the truck bed of a dump truck. Generally, a spool moves within a hydraulic valve between a raise location wherein the flow of hydraulic fluid to a cylinder raises the truck bed and a lower location wherein the flow of hydraulic fluid from the cylinder lowers the truck bed. Preferably, a neutral location is provided wherein there is no flow of hydraulic fluid to the cylinder and the truck bed remains stationary. A control means is provided to adjust the spool among its raise, neutral and lower locations. Often, a pull-out cable is provided which is fastened to the dump truck body and one end of the valve spool. This cable is adjusted so that when the truck bed reaches its maximum desired height, the cable moves the spool out of the raise location.
When the truck bed is in the raised position, the pull-out cable may be exposed. If a worker servicing the truck bed accidentally engages the cable, the spool could be moved from its neutral location to its lower location, causing the truck bed to fall. This causes a potential safety risk to a worker servicing the truck bed. Consequently, there is a need for a safety device which prevents the accidental lowering of a raised truck bed.
A safety device to prevent inadvertent transmission of forces from the pull-out cable to the spool is disclosed in Glomski, U.S. Pat. No. 4,029,359. A hollow hub extends from the valve housing and holds a sleeve which is slidingly engaged therein. The sleeve is connected to the spool and can move the spool to the neutral location when the pull-out cable is engaged. Stop means provided in the hub prevent the pull-out cable from further extending the sleeve. The hollow hub is fixed to the housing and forms an integral part thereof.
Because the hollow hub is an integral part of the housing, the Glomski safety device cannot be used as a field replacement for a hydraulic valve having no safety device. To use the Glomski safety device, one might replace the entire hydraulic valve mechanism. Thus, there is a need for a safety device which can be added to existing hydraulic valve mechanisms to prevent the accidental lowering of a raised truck bed.